Directive antenna system



Aug. 20,1946. E. BRUCE 25405,@@2

DIRECTIVE ANTENNA SYSTEM i 5yd-jl.

A T ron/v5 V E. BRUCE DIRECTIVE y.ALNTENIIMvsYsTvElvf '2 sheets-sen] 2 l Filed Jan. 19, 1944 FIG-5 SH/F TER Slfl/FTER A Tron/viv Patented Aug. 20, 1946 riclephone Laboratories, Incorporated,

New

York, N. Y., a corporation of New York Application January 19, 19441, Serial No. 518,791 Y This invention relates to `rphase Shifters and particularly te phase shiftersof the dielectric zone plate type used inY directive single zone and multiple zone antenna systems.

As disclosed in my copending application, Se-

nai No. 400,319 med June y28, 1.941,9'. 10W attenuation dielectric plate may be utilized for changing, without reflection loss, the phase of a Wave component passing through the plate nearly 180 degrees relative to that of a Icomponent propagated along an adjacent path in the ether having a length 'equal to the physical thickness of the plate. While, as explained in the abovementioned application, the reectionless. phase reversing plate is highly ruseful in microwave transmission and antenna systems, it now appears advantageous also to employ in certain radio systems dielectric means for securing WithoutA vreiiectio'n loss,V 'any' desired relative phase shift. In'accordance with the present invention,

15 Claims. (Cl. Z50-11) a pair of low attenuation dielectricplates ora i single low attenuation dielectric plate is `used to obtain, Without reflection loss, any desired phase shift.

In addition, as disclosed in my aforementioned copending applicationjand in Patents 2,043,347

granted on June 9, 1936, to A. G. Clavier et al., and 2,159,553 granted on August 15,` 1939 to applicant, highly directive antenna action may be secured by utilizing with a substantially nondirective primary antenna element a plane grating having one or more zones. The grating functions' to convert the divergent beams into par allel beams. In Vaccordance With the Vpresent invention the gains of the single zone and multiple zone antenna systems referred to above are greatly increased.

It is one object of Ythis invention to obtain one or more dielectric plates for Vchanging the relative phase of a radiolwave anyv predetermined in Vone-half of each active zone a quadrature phase shifter constructed in accordance'` With the' invention and comprising a plane single half zone dielectric plate or a -pair of parallel half zone dielectric, plates. In accordance with another embodiment ofthe invention, thegain of the singlerzone or vmultiple lone directive antenna system disclosed.l in my aforesaid copending application and having al1 zones active, is

increased by placing a quadrature phase shifter 'constructed in accordance with the invention in one-half of each zone of the grating, rIhe quadrature phase shifter functions to change the phase vector for the associated half Zone 90` degrees, and therefore to alignV the two vectorsfor theinner and outer halves of the annular zone, ywhereby -theover-all intensity of the energ passing through the zone is increased. If, in the system just described, a single plate is employed ,as the quadrature phasel shifter, the

dielectric constant and thickness of the plate are, in, accordance Withthe invention,A such that the phase shift in the plate is 180 degrees, and the phase shift along anether pathccrresponding .in length to the path in the plate is equal to 90 degrees, that is, 180 degrees minus the predetermined desired relative' phase shift of 90 degrees. Byreason of the thickness of the plate as measuredin wavelengths in the plate, the waves impinging upon the plate and reflected at the front surface of the plate and the Waves entering the plate and reflected by the rear surface are oppositely phased with ther result that there is no reflection loss. If desired, several parallel thin plates may be used for securing, without reection, a SiO-degree phase shift in place of e, single thick plate. Thus two plates having equal dielectric constants and equal thicknesses may be used. The phase shift in each plate minus the phase shift alongja correspondent etherpath is vequal to Yonefhalf of theldesired relative phase crease the gain of a directive antenna comprising a grating. v

it is a further object of this invention to increase, in a grating-type antenna system, vthe total amplitude of the waves in each zone.

In accordance with one embodiment of the invention the gain of .the single zone or multiple zone directive antenna system disclosed inthe aforementioned patents and having one set of jalternate active zones, is Vincreased by utilizing shift of90 degrees. `The spacing between the correspondent front faces, or the correspondent rear faces, is such that the `electrical path connecting `the Vcorrespondent faces and comprising the dielectric pathin one plate and the ether path between` the plates is` 90- degrees, `whereby the yWaves reected by the two front faces cancel andthe Waves reflected by the two rear'faces of theplate cancel. Stated differently, the vector sum of the reflections from the four faces equals zero.

In addition, in accordance With the invention, the single plate phase shifter, and each plate in the double plate phase shifter, may .have a di@ electric constant and a physical thickness for securing any phase shift other than 90 degrees. The thickness of the single plate asmeasured in wavelengths in the plate is always 180 degrees or an cdd integral multiple thereof, and the spacing between correspondent faces of the plates in the double plate shifter always corresponds to 9G degrees, or an odd integral multiple thereof, so that all reflected waves are canceled.

The invention will be more fully understood from a perusal of the following specification taken in conjunction with the drawingson which like reference characters denote elements of similar function, and on which:

Fig. l is a side View of a single plate phase shifter of the invention;

Fig. 2 is a side view of a double plate phase shifter constructed in accordance with the invention;

Figs. 3 and 4 are respectively a side cross-sectional view and a front viewrof one embodiment ofthe invention comprising a multiple zone directive antenna equipped with half zone dielectric plates; and

Fig. 5 is a vector diagram used in explaining the operation of the system of Figs. 3 and 4.

Y Referring to the single plate shifter shown in Fig. l, reference numeral l denotes a plate composed of dielectric material, such as titanium dioxide-set in rubber, resin, Micarta, or a mixture of resin and beeswax. The plate rhas a physical thickness t and a dielectric constant Ep. The air medium in which the plate is immersed has a dielectric constant En equal to unity. Numerals 2 and 3 denote, respectively, the front and rear faces of plate I and numeral 4 designates the advancing wave front of an incoming wave. The typical or representative components 5, 6, l, 8, 9 and l@ in the wave front have, for the wave front position illustrated, the same phase 6. The reference character VGe denotes the go or forward path traversed by component 6 in reaching the front face E and the character Re denotes the return path followed by component after reiiection-by the front face 2. Similarly, the reference characters G7 and Rv denote, respectively, the go and return paths for component? which enters the plate and is reflected by the rear face 3, Reference characters Gs and G9 denote, respectively, the go path of component 8 which passes through the plate and component S which avoids the plate.

In operation, considering the reflected components 6 and 7, both components undergo a phase shift of NIS in reaching the plate. Component 6 does not undergo a phase reversal upon reflection at the front face 2 since the wave at this face is passing from a rare to a dense medium. lOn the other hand component 1 undergoes upon reflection at the rear face 3 a phase reversal since the Wave is passing from a dense to a rare medium. On the drawings er, equal to 180 degrees, represents the phase reversal. In addition, component 'I undergoes a shift of 29p in traversing the plate l twice. The thickness t and the constant Ep-are selected so that 6p equals 180 degrees, Ep being unequal to unity. Stated differently, the thickness t equals Where Ap is the Wavelength as measured in the 4 dielectric forming the plate, and therefore does not equal where la is the wavelength as measured in the air. Hence we have for component 6 a phase Achange 0e and for component 'l 01-6= (360+ 180) degrees (3) Since components 6 and 'l arriving over paths Rs and Rv at the front 4 are oppositely phased they cancel and reection is eliminated.

Considering components Ga and G9, component Gs undergoes a phase shift of in reaching the plate and, in the plate, a phase shift of 0p. The component 9 undergoes a phase shift and a phase shift 6a in moving along an ether path having a length equal vto the plate thickness t, as measured in wavelengths in the air. Hence the desired or nal relative phase shift for components 8 and 9 is @zap-@S degrees-0a (4) It follows that any desired relative phase shift may be secured, without reiiection loss, by selecting a plate having a dielectric constant and a 4physical thickness, as measured in wavelengths in the air, such that e equals whereby @p equals 180 degrees and 0s equals 180 degrees minus the desired phase shift i To illustrate, if Ep has a value such that substituting-this 1121112013.. 211e 12:0 12), we have Y rarita I y T2-1V Q) Accordingly, a plate having 'a dielectric constant of v4 and a thickness of a quarter air wavelength is a lossless quadrature phase shifter. In one system actually tested and utilizing an operating air wavelength of Y11.2 centimeters, a plate composed rof `resin v and beeswax and having a thickness of 2.3 centimeters, functioned satisfactorily. T o secure a phase shift of' 135 degrees, thats,V 2

withoutreflection loss thefconstant Ep must equal 16 by Equation 13 where m=0, and Y must equalV In general,v for any desired relative phase shift,

the relation between the thickness t and the the plates is such that the length of the path @ps between the corresponding'front faces2, or between the rear faces 3,'is 90 degreesor'an -odd integral multiple thereof. Expressed mathematicallyv n i Y Y y 275222; e v Xp--l--QQ degrees-tZm-I-l) (17) Where m is any integer including zero, or

+0,=9c degrees= 2m+ 1) (1s) where 0s is the phase shiftfcorresponding to the ether path between the plates. e Numerals 5,8, 9, 10, 21, 22, 23 andlf24- denote components in the wave front ll.V As indicated-by the 'go'and return paths G21 and R21, component 2l is reflected bythe-front face 20)?J plate P1.V Similarly, as shown by the paths G22 and R22 cornponent 22 is reected by the front face 2 of plate P2. VThese components are not changedin phase Yupon reflection. Component 23 is, as indicated by the lpaths G23 and R23, reflected Witha phase yreversal bythe rear face 3.0i 'plate P1 and-com? 21112120111 y 25) and 26) 6 ponent 24 is similarly'relected bythe rear face 3 of plate P2, as shown by thepaths G21 and R21. Considering components 21 and 22, we have for component 2| a phase shift and the reflected Vcomponents 21 and 22 cancel each other.

Considering components 23 and 24, We have for component 23 el 01 ?2 3=2+"+0f+6+2 24) =o.+2e+o, (25) where-,as in-Fig. 1, ylrrequals degrees.

For component 24 we have @a=+e+e+e+e+e+240.4% (25A) =e44e+2e+e l i-lence reflected components 23'and 24 cancel each other. Considered diferentlyjthe vector ,sum'of components 21, 22,v 23 and 24equals. zero.

In this connectionit should be pointedout that the plates are preferablycomposed of dielectric materials in which Athe energy losses` are negligible, in order to secure maximum cancellation of the reected waves. Accordingly, by spacing the plates a critical distance dependent upon the thickness t of each plate, as measured in wavelengths in the dielectric, reflection is eliminated.

Referring tocomponent 8 which passes through both plates and component 9 which avoids both plates. the relative phase shift i1 is Substituting from Equation 1.0

If desired, three or more dielectric plates having different thicknesses and different dielectric constants may be used to secure a non-reflective phase shifter. The spacings between plates should be such that the vector sum, as measured at the iirst or initial surface, of the reections from all surfaces equals or approaches zero. The phase shift obtained equals the total thickness of the plates as measured in wavelengths in the plates minus the total thickness as measured in wavelengths in the air.

Referring to Figs. 3 and 4, numeral 3l! denotes a drum-type reflector similar to that disclosed in my aforementioned patent and copending application, the primary dilerence being that the drum opening is circular instead of oval. The drum 3l] comprises a cylindrical wall 3i and an end plane reector 32. Numeral 33 denotes a translation device, such as a transmitter or a receiver, which is connected to a Wave guide 34 having an end aperture 35 constituting a sccalled point source or collector. The device 33 is mounted on the inactive side of reflector plate 32 and inside the compartment 35 formed by the extension of the drum and the cover member 3l. Reference numeral 38 denotes a grating positioned in the drum opening and having a focus 39, an axis and a focal length d measured along the axis. The grating 3B comprises the concentric annular zones A, B and C, each having an inner half zone :c and an outer half zone y. The primary antenna or aperture is positioned at the focus 39 of the grating. In accordance with the disclosure in my copending application, zone B is equipped with a full zone dielectric plate 40 Which functions to reverse the phase of the vector for the zone without reflection loss. As explained in my patent mentioned above, the inside surface of Wall 3l and the areas of reflector 32 facing ,zones A and C are lined In accordance with the present In operation, assuming the system of Figs. 3 and 4 is employed for receiving energy, the incoming Wave lhaving `a wave front parallel to the drum opening and grating 38 passes through zones A, B and C. The Waveletsentering air zones A and C are focused upon and arrive `in'phase at the aperture 35; and the wavelets in zone B are reversed in phase and .arrive at aperture in phase with the .Wavelets from zones A and C. As will now be explained the quadrature phaseshifter 42 functions to increase the total intensity of the energy passing through eachzone.

Referring to Fig. 5, and assuming for the moment that the half zone plates 42 are omitted, the phase vectors 50 of the wavelets in any zone as, for example, zone C and passing along the extreme opposite boundaries of the zone are oppositely directed, and the components passing through the intermediate zone portions have slightly different phase vectors so that the Wavelet vectors form a semicircle the diameter 5| of which is the vector resultant for the full zone. The zone vector 5I may b e considered as comprising two quadrature half 'zone vectors r'-52 and 53 representing, respectively, the inner and youter half zones :l: and y. Assuming further that zone B is equipped with a metallic zone plate, yas disclosed in my aforementioned patent, the oppositely phased Wavelets of zone lBare eliminated and the vectors 5l of zones A and C combine to give an over-all vector resultant 54. If zone B is equipped with a dielectric phase shifter, as in Figs. 3 and 4 and in the system of my copending application, the vectors of zones A, B and C combine in phase to produce the much larger vector resultant 55. With a quadrature phase shifter in the inner half zone x, the vector 52 for this half zone is rotated degrees to the position denoted by numeral 56, and the two half zone vectors are rendered colinear. As a result, the length of the zone vector is increased and the gain of the zone enhanced, the sum denoted by numeral 5l of vectors 53 and 56 being greater than the length of vector 5l. All the parallel zone vectors 51 combine to produce the resultant vector which is much longer than the Vectors 54 and 55 for the prior art systems. Hence, in accordance with the invention, the gain of each active zone is increased; and thegain of the entire grating or system is relatively great as compared to the prior art arrangements. 'If desired, a double plate quadrature phase shifter such as-that shown in Fig. V2 may be used in place ofthe single plate shifter 42.

In the system of Figs. 3 and 4, and in-the diagram of Fig. 5, it has 'been assumed that the primary antenna 35 is a point source. If a dipole is used at the focus of the grating, the plates 40 and 42 are preferably orbicular instead of circular, in accordance With the disclosure in my copending application, the minor and major diameters or dimensions of each plate being diferent by an amount equal to the dipole length. Y Although the invention has been described in connection with certain embodiments, it is to-be understood that it is not to be limited-tothe described embodiments inasmuch as other apparatus may be Vsuccessfully utilized without exceeding the scope of the invention.

What is claimed is:

1. A phase shifter Afor passing a wave of given v Wavelength and V,for changing /Without reflection iloss the phase of said wave, said shifter'being composed of dielectric material 4and rhaving at leasttwo. faces extending perpendicular .t0 `the 'direction of said wave, the path aligned with said direction and connecting said faces being equivalent to a multiple, including the integer one, of 90 degrees, and the difference between the dimension alonfI said path of the material as measured in wavelengths in the material and the dimension as measured in wavelengths in the air being equivalent to a phase shift smaller or greater than 180 degrees.

2. A phase shifter for securing a desired phase shift without reflection loss comprising a plate composed of dielectric material, said plate having a thickness of a half wavelength as measured in the plate a thickness equal to a half wavelength minus said desired phase shift, measured in the air.

3. A S30-degree phase shifter c niprising a dielectric plate having a dielectric constant equal to four and a thickness of a half wavelength as measured in the plate and a quarter wavelength as measured in the air.

li. A phase shifter for securing a desired phase shift without reflection loss comprising a pair of parallel dielectric plates, the spacing between plates being equivalent to 90 electrical degrees minus the electrical degrees corresponding to the thickness of one plate measured in wavelengths in the plate.

5. A phase shifter for securing a desired phase shift without reiiection comprising a plurality of plates each composed of dielectric material and having two faces extending parallel to an incoming wave front, the difference in electrical length between the paths connecting` said wave front and any one of said faces and connecting said wave front and another of said faces being 90 degrecs, and the difference between the total thickness of said plates as measured in wavelengths in the air and as measured in the materials composing said plates being equal to the desired phase shift.

G. A non-reflective phase shifter for securing a desired phase shift comprising a plurality of dielectric plates spaced along the direction of an incoming wave and each having a pair of faces angularly related to said direction, the electrical lengths of the paths along said direction between the front face of the plate first traversed by the incoming wave and each f the other faces of said plates being related to the thickness and dielectric constants of said plates, whereby the vector sum as at said front face of all waves reflected by all of said faces equals Zero substantially.

7. A phase shifter for securing a desired phase shift with reflection cancellation comprising a pair of parallel dielectric plates having the same thickness and the same dielectric constant, the difference :between the thickness of each plate as measured in wavelengths in the plate and the ld thickness of each plate as measured in wavelengths in the air being equal to one-half' the desired phase shift.

8. A phase shifter in accordance with the preceding claim, each of the two paths connecting corresponding faces of the plates having a length equivalent to 9G degrees.

9. In combination, a `niultipie sone grating comprising a plurality of concentric full-Zone diffraction plates positioned in a, first set of alternate Zones of said grating and each having a focus, means at said focus for energizing one Set of alternate Zones of said grating with similarly phased waves and the other or second set of alternate Zones with oppositely phased waves, and quadrature phase shifting means in ene-half of each Zone of one set of alternate zones.

l0. A combination in accordance with claim 9, said means comprising a circular half Zone dielectric plate.

ll. A combination in accordance with claim 9, said means comprising a half zone dielectric plate positioned in the inner half of the zone.

l2. A combination in accordance with claim 9, and quadrature phase shifting means in one half of each Zone of the second set of alternate Zones.

13. In an antenna system, a drum reflector having an opening, a multiple zone grating positioned in said opening and comprising a plurality of concentric full-Zone diffraction plates having a common focus, a primary antenna at said focus, and phase shifting means positioned in each Zone.

14. In combination, an antenna element at a given point for transmitting or receiving a wave having a given wavelength and a circular wave front, diffraction means for changing an incoming plane wave front into a circular wave front and for changing an outgoing circular wave front into a plane wave front, said diffraction means comprising at least one full-zone plate and at least one half-Zone dielectric plate each having a face parallel to said plane wave fronts, the difference in the distances from said point to the edges of said full-Zone plate face farthest from and nearest to said point being equal to onehalf of said wavelength, the difference in the distances from said point to the edges of the half- Zone plate face farthest from and nearest to said point being equal to a quarter of said wavelength, one of the aforementioned edges of said full-Zone plate face and one of the aforementioned edges of said half-zone plate face being at substantially the same distance from said point.

15. A combination in accordance with claim 14, said half-zone plate having a thickness of a halfwavelength as measured in the plate and a quarter wavelength as measured in the air.

EDMOND BRUCE. 

